Universal production ball grid array socket

ABSTRACT

A universal production ball grid array socket is provided for use with a ball grid array package. The socket will receive a ball grid array package and in turn can be mounted or plugged into an underlying circuit board. One embodiment of the socket includes a tulip-shaped contact which is capable of receiving ball grid array ball leads of various diameters. Another embodiment of the socket includes a ball receiving contact capable of clasping an inserted ball grid array ball lead. In still another embodiment the universal production ball grid array socket is translucent allowing for visual inspection of a ball grid array package and ball grid array socket combination. Methods are provided for mounting a plurality of ball leads onto the bases of a plurality of ball receiving contacts after the contacts have been mounted within the universal production ball grid array socket. Transition pins are also provided for allowing most integrated circuits to be used with the sockets of the subject invention and for adapting a ball grid array package to be capable of repeated engagement and disengagement of sockets of the subject invention.

The application is a continuation-in-part application of U.S. patentapplication Ser. No. 08/626,320 filed Apr. 2, 1996, now U.S. Pat. No.5,730,606.

BACKGROUND OF THE INVENTION

The subject invention relates to a universal production ball grid arraysocket for establishing solderless connections between the conductiveballs of a ball grid array package and a printed circuit board. Moreparticularly, the lead balls of a ball grid array package can besolderlessly mounted within the contacts of the ball grid array socket.

There currently exists several different methods for packagingsemi-conductor devices. One popular type of semi-conductor packaging isreferred to as a quad flat pack (QFP), which is a type of peripherallead package. A new type of packaging technology is referred to as theball grid array (BGA). The ball grid array was introduced byInternational Business Machines Corp. (IBM) and includes a number ofbenefits, including small package size, good yield, better electricalperformance, and lower profiles, among others.

The BGAs generally place conductive ball leads over the entire surfaceof a chip, instead of just around the edges. Thus, BGA packages allowsystem designers to place more leads in a given package size usinglooser tolerances than peripheral lead type packages such as the quadflat pack. Therefore, board producers are not required to use the finepitch spacings that are now necessary for high lead count packages.Also, BGAs have finer pitch spacings than pin grid arrays (PGA), sincethe solder balls do not have the coplanarality problem associated withthrough-hole PGAs. In the prior art, the electrical connection betweenthe BGA package and underlying PC board was generally provided bysoldering the ball leads which are located underneath the BGA packageonto pads which are provided on the upper surface of printed circuitboards.

In many applications the soldering of the ball leads of the ball gridarray package to the printed circuit board is undesirable. For example,it is impossible to visually locate a short or ground between the ballgrid array package and printed circuit board. Usually, an expensiveX-ray technique is required to inspect the connections since the ballleads are hidden under the ball grid array package. Further, theincreasing number of ball leads being provided by ball grid arraypackages makes the soldering of the ball grid array packages to printedcircuit boards more difficult.

Accordingly, in the prior art, an improved connector has been developedwhich is designed to eliminate the need for the soldering the ball leadsof a BGA package to a printed circuit board. One example of a devicewhich satisfied this criteria is the fuzz ball socket. The fuzz ballsocket comprises a plurality of electrical contacts mounted within aninsulated housing. Each contact resembles a brillo pad, made up ofindividual gold plated wires, forced into a through hole of theinsulated housing. Using a great deal of pressure the fuzz ball socketcan be forced down and bolted onto a PC board, thereby providing theproper electrical contact. The BGA package is then placed in the fuzzball socket, a metal cover is placed on top of the BGA package and agreat deal of pressure is exerted on the cover to force the ball leadsof the BGA package into the proper electrical connection with the fuzzball socket.

In many applications, the necessity of using a great deal of pressure toforce the ball leads of a BGA package into a fuzz ball socket isundesirable. For example, the number of ball leads placed on a BGApackage are increasing, thereby making the mounting of a BGA packagewithin a fuzz ball socket increasingly difficult since greater andgreater pressure is required to create a proper electrical connection.Further, the great force required to push the ball leads into contactwith the fuzz ball socket creates wear on the BGA ball leads andincreases the likelihood of distorting the ball leads. Additionally, themanufacture of a fuzz ball is very expensive since wire must beindividually wired into each through hole.

BGA packages are often provided with eutetic solder ball leadscomprising 63/37 tin/lead solder. Unfortunately, 63/37 tin/lead solderis a relatively soft material which is readily distortable. Mostsolderless connections, as with the aforementioned fuzz ball socket,rely on spring forces to maintain electrical connections. Theapplication of the spring forces to the solder ball leads may causedistortion thereof.

It is therefore an object of the subject invention to provide auniversal production ball grid array socket which eliminates thenecessity to solder the conductive ball leads of a BGA package to thecontacts of a printed circuit board.

It is another object of the subject invention to provide a universalproduction ball grid array socket which reduces the large amount ofpressure required to mount a BGA package onto a BGA socket.

It is still another object of the subject invention to provide auniversal production ball grid array socket having a unique resilientelectrical contact capable of achieving electrical connection betweenthe contact of a circuit board and the conductive ball lead of a BGApackage. In particular, a socket is disclosed having a contact whichresiliently expands to electrically engage conductive ball leads ofvarying diameters.

It is a further object of the subject invention to provide a universalball grid array socket wherein the ball grid array package is positivelylocked within the housing of the ball grid array socket therebypreventing the degradation of the electrical connection due to vibrationor other disturbance.

It is an object of the second embodiment of the subject invention toprovide a coverless universal ball grid array socket having resilientcontacts for clasping the ball leads of a BGA package therebyestablishing a relatively high retentive force and preventing thedegradation of electrical connection due to vibration or otherdisturbance.

It is an object of the third embodiment of the subject invention toprovide a coverless universal ball grid array socket having resilientcontacts for clamping the ball leads of the ball grid array packagewhere only a slight portion of the resilient contact is utilized as ameans for preventing contact slippage within the universal ball gridarray socket.

It is an object of the fourth embodiment of the subject invention toprovide a coverless translucent ball grid array socket which allows forquick and easy inspection of a ball grid array package and ball gridarray socket combination.

An additional object of the subject invention is to provide a method formounting ball leads onto a ball grid array socket.

It is yet another object of the subject invention to provide atransition adaptor for converting an unsocketable integrated circuitinto a socketable integrated circuit.

SUMMARY OF THE INVENTION

In accordance with these and many other objects, the subject inventionprovides for a universal production ball grid array socket assembly forreceiving a ball grid array package having an array of conductive ballleads. The socket assembly includes a generally rectangular,non-conductive housing having a carrier base, a plurality of upstandingside walls, and a cover. The carrier base has an upper surface, a lowersurface, and a plurality of apertures corresponding to the plurality ofconductive ball leads of the ball grid array package. Each apertureextends through the carrier base and is defined by an inner surface. Theside walls define an insert area in which the ball grid array packagecan be placed. The cover is for retaining the ball grid array packageplaced in the insert area and for forcing the ball grid array packageinto electrical contact with the ball grid array socket. A plurality oftulip-shaped conductive ball receiving contacts are provided with eachball receiving contact mounted within an aperture of the carrier base.

Each ball receiving contact includes a split collar having a pluralityof upwardly extending resilient cantilevered leaves, a plurality ofdownwardly extending cantilevered tangs, and a downwardly extendingcantilevered blade. The resilient cantilevered leaves of each ballreceiving contact are for releasably receiving and electrically engaginga ball lead of an inserted ball grid array package. The cantileveredtangs of each ball receiving contact engage the inner surface of theaperture in an interference fit. The cantilevered blade of each ballreceiving contact is for engagement with an underlying semi-conductordevice. Alternatively, a solder ball may be mounted to the bottom of thesplit collar, in lieu of the cantilevered blade, for engagement with anunderlying semi-conductor device.

In a second embodiment of the subject invention there is provided acoverless ball grid array socket assembly which clasps an inserted ballgrid array package into position. In particular, the socket assemblyincludes a generally rectangular, non-conductive carrier base having aplurality of apertures. Each aperture is defined by an inner surface andextends through the carrier base. A plurality of conductive ballreceiving contacts are provided with each contact being mounted withinan aperture of the carrier base.

Each ball receiving contact includes a base plate having an uppersurface and a lower surface, two opposing cantilevered resilient armsextending upwardly from the base plate and two opposing resilient tangsextending upwardly from the base plate for engaging the inner surface ofthe surrounding aperture in an interference fit. Each resilientcantilevered arm of the ball receiving contact has a clasping mechanismfor clasping a ball lead of an inserted ball grid array package. By thisarrangement, the ball lead of an inserted ball grid array package isretained by and electrically engaged with the ball receiving contactwithout use of a cover. A conductive ball lead may be mounted to thelower surface of the base plate of the ball receiving contact forconnection to an underlying semi-conductor device.

In a third embodiment of the subject invention there is provided acoverless ball grid array socket assembly which clasps an inserted ballgrid array package into position through a plurality of conductiveresilient ball receiving contacts. In particular, the socket assemblyincludes a generally rectangular, non-conductive carrier base having aplurality of apertures. Each aperture is defined by an inner surface andextends through the carrier base. A plurality of conductive ballreceiving contacts are provided with each contact being mounted withinan aperture of the carrier base.

Each ball receiving contact includes a base plate having an uppersurface and a lower surface, two opposing cantilevered resilient armsextending upwardly from the base plate and four resilient tabsprojecting slightly above the upper surface of the base plate forengagement with the inner surface of the surrounding aperture in aninterference fit. Each resilient cantilevered arm of the ball receivingcontact has a clasping mechanism for clasping a ball lead of an insertedball grid array package. By this arrangement, the ball lead of aninserted ball grid array package is retained by and electrically engagedwith the ball receiving contact without use of a cover. A conductiveball lead may be mounted to the lower surface of the base plate forconnection to an underlying semi-conductive device.

In a fourth embodiment of the subject invention there is provided acoverless translucent ball grid array socket assembly which clasps aninserted ball grid array package into position through a plurality ofconductive resilient ball receiving contacts. In particular, the socketassembly includes a generally rectangular translucent non-conductivecarrier base having an upper surface, a lower surface and a plurality ofapertures. Each aperture extends through the carrier base and is definedby an inner surface. A plurality of conductive ball receiving contactsare provided with each contact being mounted to the lower surface of thecarrier base and extending within an aperture of the carrier base.

Each ball receiving contact includes an elongated base plate having atop surface, a bottom surface, and a length which is greater than thediameter of the carrier base aperture. Portions of the top surface ofthe elongated base plate are mounted to the lower surface of the carrierbase. The ball receiving contact further includes two opposingcantilevered resilient arms which extend upwardly from the elongatedbase and into an aperture of the carrier base. Each resilientcantilevered arm has a clasping mechanism for clasping a ball lead of aninserted ball grid array package. By this arrangement, the ball lead ofan inserted ball grid array package is retained by and electricallyengaged with the ball receiving contact without use of a cover. The ballreceiving contact may further include a conductive ball lead mounted tothe bottom surface of the elongated base plate for attachment to aprinted circuit board.

A method for the subject invention is provided for mounting a pluralityof ball leads onto a ball grid array socket comprising the steps ofmounting a plurality of ball receiving contacts within a plurality ofapertures of a carrier base, the carrier base having a bottom surfaceand each ball receiving contact mounted within a corresponding aperturesuch that the bottom surface of each ball receiving contact is flushwith the bottom surface of the carrier base to create a contact gridhaving contact areas and non-contact areas; inverting the carrier base;and depositing a plurality of ball leads onto the inverted carrier base,each ball lead deposited on the bottom surface of each ball receivingcontact in the contact grid.

The above-described contacts can be modified to be formed with a solderball mounted to the respective bottom thereof, instead of a cantileveredblade or ball lead. The solder ball will allow for easy mounting of thecontact to a desired location.

Also, transition pins are provided for converting an unsocketableintegrated circuit (not necessarily a ball grid array package) into asocketable integrated circuit. As used herein, "unsocketable" is definedto describe an integrated circuit which is not formed to be received byany of the sockets disclosed herein, for example, an integrated circuithaving lands rather than ball lead contacts. Also, the term"unsocketable" is intended to describe a ball grid array package havingball lead contacts formed from a relatively soft material, typicallywhich is solder, and not well-suited for being repeatedly received byany of the sockets disclosed herein. In contrast, the term "socketable"is intended to describe a device which is formed for and well-suited tobe received by the sockets disclosed herein.

In one embodiment of the transition pins, surface mount transition pinsare provided. The pins have a planar surface at one end for mountingonto the leads of an unsocketable integrated circuit and a truncatedspade-shaped head at the opposing end dimensioned to be engaged by thecontacts disclosed herein. Preferably, the transition pins are formedfrom a copper alloy, preferably brass, which is a relatively hardmaterial with good conductive properties and capable of withstandingrepeated engagement and disengagement with the sockets of the subjectinvention.

In a second embodiment of the transition pins, the transition pins areformed with a planar surface at one end and the same truncatedspade-shaped head at the opposing end as the transition pins of thefirst embodiment, but have elongated bodies for mounting onto andthrough a non-conductive adaptor board. A ball grid array package havingsolder ball leads may be soldered onto the planar ends of the transitionpins, and the entire assembly, including the ball grid array package andthe adaptor board, may be securely received by any of the socketsdisclosed herein. Again, the transition pins are preferably formed froma copper alloy, such as brass, to provide both hardness and goodconductive properties.

In summary, there is provided a universal production ball grid arraysocket assembly having tulip-shaped ball receiving contacts which allowball grid array packages having ball leads of varying diameters to besolderlessly mounted to an underlying circuit board.

In summary, the second embodiment of the subject invention provides acoverless universal ball grid array socket having ball receivingcontacts which clasp the ball leads of the ball grid array package witha substantial retentive force.

In summary, the third embodiment of the subject invention provides acoverless universal production ball grid array socket having claspingball receiving contacts which have four slightly projecting tabs formounting the ball receiving contacts within the universal productionball grid array socket of the subject invention.

In summary, the fourth embodiment of the subject invention provides atranslucent coverless ball grid array socket which allows for quick andeasy inspection of a ball grid array package and a ball grid arraysocket combination.

In summary, a method for the subject invention is provided for mountinga plurality of ball leads onto a ball grid array socket.

Other objects of the invention will become apparent from the followingdescription in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of the ball grid array socket ofthe subject invention.

FIG. 1A is a side elevational view, partially in section, of a ball gridarray package taken along line 1A--1A in FIG. 1.

FIG. 2 is an exploded perspective view, partially in section, of a firstembodiment of the subject invention.

FIG. 3 is a perspective view of a tulip-shaped ball receiving contact ofthe first embodiment of the subject invention.

FIG. 4 is a side elevational view of a tulip-shaped ball receivingcontact of the first embodiment of the subject invention.

FIG. 5 is a front view of a tulip-shaped ball receiving contact of thefirst embodiment of the subject invention.

FIG. 6 is a top plan view of a tulip-shaped ball receiving contact ofthe first embodiment of the subject invention.

FIG. 7 is an exploded side elevational view, partially in section, of aball grid array lead disengaged from a tulip-shaped ball receivingcontact of the first embodiment of the subject invention.

FIG. 7A is a side elevational view, partially in section, of a ball gridarray lead engaged with a tulip-shaped ball receiving contact of thefirst embodiment of the subject invention.

FIG. 8 is an exploded perspective view of a ball grid array leaddisengaged from a dual contact of the second embodiment of the subjectinvention.

FIG. 9 is a side elevational view of a dual contact of the secondembodiment of the subject invention.

FIG. 10 is a side elevational view, partially in section, of a ball gridarray lead engaged with a dual contact of the second embodiment of thesubject invention.

FIG. 11 is an exploded perspective view of a ball grid array leaddisengaged from a ball receiving contact of the third embodiment of thesubject invention.

FIG. 12 is a side elevational view, partially in section, of a ball gridarray lead engaged with a ball receiving contact of the third embodimentof the subject invention.

FIG. 13 is an exploded perspective view of a ball grid array leaddisengaged from a ball receiving contact of the fourth embodiment of thesubject invention.

FIG. 14 is a side elevational view, partially in section, of a ball gridarray lead engaged with a ball receiving contact of the fourthembodiment of the subject invention.

FIG. 15 is a perspective view of the ball receiving contact of thefourth embodiment of the subject invention with continuous front andrear edges.

FIG. 16 illustrates a method of mounting ball leads to a ball grid arraysocket utilizing a solder resist.

FIG. 17 illustrates a method of mounting ball leads to a ball grid arraysocket utilizing a dry resist.

FIG. 18 is a perspective view of the tulip-shaped ball receiving contactof the first embodiment of the subject invention modified to be formedwith a solder ball mounted to the bottom of the contact.

FIG. 19 is a side elevational view, partially in section, of the firstembodiment of the transition pin surface mounted to an integratedcircuit.

FIG. 20 is a side elevational view, partially in section, of the secondembodiment of the transition pin mounted in an adaptor board.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 1A, the present invention is indicatedgenerally by the reference numeral 10. A ball grid array package 12typically consists of a semi-conductor device 14 and a plurality of ballleads 16 extending downwardly from the bottom surface 18 of thesemi-conductor device 14.

The present invention 10 includes a non-conductive base 20 and aplurality of walls 22 extending upwardly from the base 20. The base 20and the plurality of walls 22 define an insert area 24 in which the ballgrid array package 12 can be placed. A plurality of apertures 26 extendthrough the base 20 of the ball grid array socket 10. Additionally, thepresent invention includes a cover 28 which can be mounted to the uppersurfaces 30 of the plurality of walls 22 through a plurality of screws32. In particular, the plurality of screws 32 are screwed through aplurality of apertures 34 which extend through the cover and into aplurality of threaded holes 36 which extend into the plurality of walls22.

As explained in further detail below, a ball grid array package 12 canbe mounted to the ball grid array socket 10 of the subject invention byplacing the ball grid array package 12 in the insert area 24 of the ballgrid array socket 10. The cover 28 is then mounted on top of the ballgrid array package 12 and ball grid array socket 10 combination by theplurality of screws 32.

Turning to FIG. 2, the cooperation between a ball lead 16 of the ballgrid array 12 and an aperture 26 of the ball grid array socket 10 isshown in greater detail. The aperture 26 of the ball grid array socket10 is tapered and is defined by an inner surface 40. The taperedaperture 26 has a maximum diameter adjacent the upper surface 42 of thebase 20 and has a minimum diameter adjacent the lower surface 44 of thebase 20. A tulip-shaped ball receiving contact 46 engages the innersurface of the tapered aperture 26 in an interference fit. As explainedin further detail below, as each ball lead 16 of the ball grid array 12enters its respective tapered aperture 26 in the ball grid array socket10 the ball lead 16 engages the upper portion of the tulip-shaped ballreceiving contact 46.

Turning to FIGS. 3-6, the tulip-shaped ball receiving contact 46 of thefirst embodiment of the subject invention is shown in greater detail.The tulip-shaped ball receiving contact 46 includes a split collar 48from which a plurality of upwardly extending cantilevered leaves 50extend. The tulip-shaped ball receiving contact 46 also includes aplurality of cantilevered tangs 52 and a single cantilevered blade 54extending downwardly from the split collar 48. The tulip-shaped ballreceiving contact 46 may be formed from any known resilient conductivematerial. One example being heat-treated beryllium copper.

As seen in FIGS. 3 and 6, each leaf 50 of the tulip-shaped ballreceiving contact 46 has a shallow V-shaped configuration with the apexof the V extending toward the center axis of the split collar 48. Theupper inner portions 56 of each leaf 50 define the primary contactpoints between the tulip-shaped ball receiving contact 46 and aninserted ball lead 16 of a ball grid array package 12.

The plurality of tangs 52 extend downwardly from the split collar 48.Each tang extends beyond the outer surface 60 of the split collar 48.The tangs 52 become compressed when the tulip-shaped ball receivingcontact 46 is inserted into the tapered aperture 26 of the base 20. Thiscompression of the tangs 52 results in an interference fit between thetulip-shaped ball receiving contact 46 and the inner surface 40 of thetapered aperture 26. This interference fit prohibits shifting of thetulip-shaped ball receiving contact 46 during engagement anddisengagement with a ball lead 16 of the ball grid array package 12.

The cantilevered blade 54 extends downwardly from the split collar 48and includes a projection 62. This cantilevered blade 54 can be pluggedinto a socket of an underlying device or bent over and bolted to anunderlying circuit board. Additionally, the blade 54 can be bent overand trimmed so that only the projection 62 is present. The projection 62can then be soldered to an underlying electrical component.

Referring to FIGS. 7 and 7A, the ball grid array ball lead 16 andtulip-shaped ball receiving contact 46 combination is shown. In general,the ball lead 16 of the ball grid array package 12 and the ballreceiving contact 46 move from a disengaged position where the ball gridarray package 12 is inserted into the insert area 24 of the ball gridarray socket 10 (FIG. 1) to an engaged position where the ball gridarray package 12 is clamped into place by mounting the cover 28 onto theball grid array package 12 and ball grid array socket 10 combination.

Turning to FIG. 7, the disengaged position of the tulip-shaped ballreceiving contact 46 and the ball lead 16 is shown. At the disengagedposition the ball lead 16 is spaced a distance from the tulip-shapedball receiving contact 46. The resilient leaves 50 of the tulip-shapedball receiving contact 46 are at rest and spaced apart at a distanceless than the diameter of the ball lead 16 of the ball grid arraypackage 12. The upper most portions of the cantilevered leaves 50 areflush with the upper surface 42 of the base 20. The cantilevered blade54 of the tulip-shaped contact 46 projects below the lower surface 44 ofthe base 20 for engagement with an underlying electrical device.

Turning now to FIG. 7A, the engaged position of the tulip-shaped ballreceiving contact 46 and the ball lead 16 is shown. In the engagedposition the ball lead 16 engages the upper inner portions 56 of thecantilevered leaves 50 of the tulip-shaped ball receiving contact 46. Inparticular, the resilient leaves 50 bend away from the ball lead 16 thatthe tulip-shaped ball receiving contact 46 is receiving. Accordingly,the upper inner surface 56 of each leaf 50 wipes the ball lead 16 andengages in an electrical connection with the ball lead 16. As a result,a plurality of electrical connections of high integrity are created asthe ball lead 16 is received within the plurality of leaves 50 of thetulip-shaped ball receiving contact 46. It should be noted that theleaves 50 never bend far enough so as to exceed the elastic limit of thematerial from which the tulip-shaped ball receiving contact 46 is madeor bend far enough so as to come into contact with the inner surface 40of the tapered aperture 26.

Turning to FIGS. 8-10, the second embodiment of the ball receivingcontact of the subject invention is illustrated and is designatedgenerally by the reference numeral 70. The dual contact 70 comprises abase 72 having an upper surface 74 and a lower surface 76. A pair ofcantilevered resilient opposing arms 78 and a pair of cantileveredresilient opposing tangs 80 extend upwardly from the upper surface 74 ofthe base 72. The lower surface 76 of the base may be in the form of awell 82. A ball lead 84 may be soldered onto the lower surface 76 of thebase 72 after the dual contact 70 has engaged the inner surface 40 ofthe tapered aperture 26 in a strong interference fit. The dual contact70 may be formed from any known resilient conductive material. Oneexample being heat-threaded beryllium copper.

As shown in FIG. 8, each resilient upwardly extending cantilevered arm78 further includes a clasping mechanism. The preferred claspingmechanism is a tapered aperture 86 disposed adjacent the free end of thecantilevered arm 78.

The opposing pair of resilient tangs 80 are spaced apart at such adistance so as to ensure a strong interference fit between the dualcontact 70 and the inner surface 40 of the tapered aperture 26. Inparticular, the dual contact 70 is inserted through the tapered aperture38 adjacent the upper surface 42 of the base 20 of the ball grid arraysocket 10. The dual contact 70 is pressed into the aperture 26 until thebase 72 of the dual contact 70 is flush with the lower surface 44 of thebase 20 of the ball grid array socket 10. At this point the tangs 80 areengaged in an interference fit of sufficient strength with the innersurface 40 of the aperture 26 so as to ensure that the dual contact 70remains in place as it engages and disengages a ball lead 16 of the ballgrid array package 12. After the dual contact 70 engages the innersurface 40 of the tapered aperture 38 a ball lead 84 may be solderedonto the base 72 of the dual contact 70. The ball lead 84 may then bemounted to an underlying circuit board. The soldering of the ball lead84 onto the base 72 of the dual contact 70 further strengthens theengagement of the dual contact lead 70 with the base 20 of the ball gridarray socket 10 since the ball lead 84 is of a greater diameter than theminimum diameter of the tapered aperture 26 adjacent the lower surface44 of the base 20. In other words, the ball lead 84 cannot be pulledthrough the tapered aperture 26 as the ball lead 16 is removed from thedual contact 70.

Referring to FIGS. 8 and 10, the disengaged and engaged positions of theball grid array ball lead 16 and of the dual contact 70 are shown. Ingeneral, the ball lead 16 and dual contact 70 are in a disengagedposition when the ball grid array package 12 is placed into the insertarea 24 of the ball grid array 10 (see FIG. 1). The ball lead 16 anddual contact 70 are in an engaged position when a slight force isexerted on the ball grid array package 12 causing each dual contact 70to clasp its respective ball lead 16.

Turning to FIG. 8, the disengaged position of the dual contact 70 andball lead 16 is shown. In the disengaged position the ball lead 16 isspaced a distance from the dual contact 70. The pair of opposingresilient arms 78 of the dual contact 70 are at rest and spaced apart ata distance less than the diameter of the ball lead 16 of the ball gridarray package 12.

Turning to FIG. 10, the engaged position of the dual contact 70 and balllead 16 is shown. In the engaged position the ball lead 16 is claspedbetween each inner surface 88 of the clasping aperture 86. In going fromthe disengaged position to the engaged position the ball lead 16initially causes the opposing arms 78 to resiliently expand away fromeach other as the ball lead 16 is inserted between them. However, whenthe ball lead 16 is pressed between each clasping aperture 86 theopposing arms 78 spring shut thus clasping the ball lead 16 between theinner surfaces 88 of the clasping aperture 86. It should be noted thatthe retentive force exerted by each dual contact 70 is significantlygreater than the initial insertion force required to press a ball lead16 into engagement with the dual contact 70. As a result, a ball gridarray socket 10 employing the second embodiment of the ball receivingcontact 70 does not require a cover to ensure proper engagement betweenthe ball grid array package 12 and ball grid array socket 10.

Turning to FIGS. 11-12, the third embodiment of the ball receivingcontact of the subject invention is illustrated and is designatedgenerally by the reference numeral 90. The ball receiving contact 90comprises a base 92 having an upper surface 94 and a lower surface 96. Apair of cantilevered resilient opposing arms 98 extend upwardly from theupper surface 94 of the base 92. Two opposing pairs of tabs 100 projectslightly from the upper surface 94 of the base 92. A ball lead 102 maybe soldered onto the lower surface 96 of the base 92 after the ballreceiving contact 90 has engaged the inner surface 40 of the taperedaperture 26 in a strong interference fit. The ball receiving contact 90may be formed from any known resilient conductive material. One examplebeing heat-treated beryllium copper.

As shown in FIG. 11, each resilient upwardly extending cantilevered arm98 further includes a clasping mechanism. The preferred claspingmechanism for the third embodiment of the ball receiving contact is abifurcated annular contact 104 disposed adjacent the free end of thecantilevered arm 98.

The opposing pairs of upwardly projecting tabs 100 are spaced apart atsuch a distance so as to ensure a strong interference fit between theball receiving contact 90 and the inner surface 40 of the taperedaperture 26. In particular, the ball receiving contact 90 is insertedthrough the tapered aperture 26 at its maximum diameter, i.e., adjacentthe upper surface 42 of the base 20 of the ball grid array socket 10.The ball receiving contact 90 is pressed into the aperture 26 until thecontact base 92 is flush with the lower surface 44 of the base 20 of theball grid array socket 10. At this point the opposing pairs of tabs 100are engaged in an interference fit of sufficient strength so as toensure that the ball receiving contact 90 remains in place as it engagesand disengages a ball lead 16 of the ball grid array package 12. Afterthe ball receiving contact 90 is engaged with the inner surface 40 ofthe aperture 26 in an interference fit a conductive lower ball lead 102may be soldered onto the lower surface 96 of the base 92. The ball lead102 may then be mounted to an underlying circuit board.

Referring again to FIGS. 11 and 12, the disengaged and engaged positionsof the ball grid array ball lead 16 and the ball receiving contact 90 ofthe ball grid array socket 10 are shown. In general, the ball lead 16and the ball receiving contact 90 are in a disengaged position when theball grid array package 12 is first placed in the insert area 24 of theball grid array socket 10 (see FIG. 1). The ball lead 16 and the balllead receiving contact 90 are in an engaged position when a slight forceis exerted on the ball grid array package 12 causing each ball leadreceiving contact 90 to clasp its respective cooperating ball lead 16.

Referring to FIG. 11, the disengaged position of the ball receivingcontact 90 and ball lead 16 is shown. In the disengaged position theball lead 16 is spaced a distance from the ball receiving contact 90.The pair of opposing resilient arms 98 of the ball receiving contact 90are at rest and spaced apart at a distance less than the diameter of theball lead 16 of the ball grid array package 12.

Referring to FIG. 12, the engaged position of the ball receiving contact90 and the ball lead 16 is shown. In the engaged position the ball lead16 is clasped between the bifurcated annular contacts 104 of theresilient arms 98. In moving from the disengaged position to the engagedposition the ball lead 16 initially causes the opposing arms 98 toresiliently expand away from each other as the ball lead 16 is insertedbetween them. However, when the ball lead is pressed between eachbifurcated annular contact point 104 the opposing arms 98 spring towardseach other thus clasping the ball lead 16 between the bifurcated annularcontact points 104 of the opposing resilient arms 98. It should be notedthat the retentive force exerted by each ball receiving contact 90 issignificantly greater than the initial insertion force required to pressa ball lead 16 into engagement with a ball receiving contact 90. As aresult, a ball grid array socket 10 employing the third embodiment ofthe ball receiving contact 90 does not require a cover to ensure properengagement between the ball grid array package 12 and ball grid arraysocket 10. Additionally, it should be noted that the tabs 100 of thethird embodiment of the ball receiving contact 90 are manufactured fromsignificantly less material than the tangs 80 of the second embodimentof the ball receiving contact 90. As a result, the third embodiment ofthe ball receiving contact 90 can be mass produced at a cost that issignificantly less than the cost to mass produce the second embodimentof the ball receiving contact 90.

Turning to FIGS. 13 and 14, the fourth embodiment of the ball receivingcontact of the subject invention is illustrated and is designated by thereference numeral 110. The ball lead receiving contact 110 comprises anelongated base 112 having an upper surface 114, a lower surface 116, afront edge 118, a rear edge 120 and opposing side edges 122, 124. Acantilevered resilient arm 126 extends upwardly from each side edge 122,124. The front and rear edges 118, 120 may have a plurality of annularprojections 128, FIG. 13, or may be a continuous arc 130, FIG. 15. Asseen in FIG. 14, the distance between the front edge 118 and the rearedge 120 is greater than the minimum diameter of the aperture 26.Accordingly, the ball receiving contact 110 does not engage in aninterference fit with the aperture 26 that it is inserted within. A dryfilm 132 is used to connect the elongated base 112 to the lower surface44 of the base 20 of the ball grid array socket 10. As a result, thereis no pressure put on the inner surface 40 of the apertures 26. This isa critical aspect of this fourth embodiment of the ball receivingcontact 110 because it allows the carrier base 20 of the subjectinvention to be manufactured from a translucent material containing ahigh percentage of glass. In particular, the lack of internal pressurecaused by the lack of the friction fittings in the apertures 26 iscritical because pressure caused by friction fittings would shatter acarrier base 20 formed from a translucent material. A ball lead 134 maybe soldered onto to the lower surface 116 of the base 112 of the ballreceiving contact 110 after the ball receiving contact 110 has beenconnected by the dry film 132 to the lower surface 44 of the carrierbase 20.

As shown in FIG. 13, each resilient upwardly extending cantilevered arm126 further includes a clasping mechanism. The preferred claspingmechanism for the fourth embodiment of the ball receiving contact 110 isa bifurcated annular contact point 136 disposed adjacent the free end ofthe cantilevered arm 126.

Referring to FIGS. 13 and 14, the disengaged and engaged positions ofthe ball grid array ball lead 16 and of the ball receiving contact 110are shown. In general, the ball lead 16 and ball receiving contact 110are in a disengaged position when the ball grid array package 12 isfirst placed into the insert area 24 (see FIG. 1) of the ball grid arraysocket 10. The ball lead 16 and ball receiving contact 110 enter into anengaged position when a slight force is exerted on the ball grid arraypackage 12 causing each ball receiving contact 110 to clasp itsrespective cooperating ball lead 16.

Turning to FIG. 14, the disengaged position of the ball receivingcontact 110 and ball lead 16 is shown. In the disengaged position theball lead 16 is spaced a distance from the ball receiving contact 110.The pair of opposing resilient arms 126 of the ball lead receivingcontact 110 are at rest and spaced apart at a distance less than thediameter of the ball lead 16 of the ball grid array package 12.

Turning to FIG. 14, the engaged position of the ball receiving contact110 and ball lead 16 is shown. In the engaged position the ball lead 16is clasped between the bifurcated annular contacts 136 of the resilientarms 126. In moving from the disengaged position to the engaged positionthe ball lead 16 initially causes the opposing arms 126 to resilientlyexpand away from each other as the ball lead 16 is inserted betweenthem. However, when the ball lead 16 is pressed between each bifurcatedannular contact point 136 the opposing arms 126 spring back towards eachother thus clasping the ball lead 16 between their bifurcated annularcontact points 136. It should be noted that the retentive force exertedby each ball receiving contact 110 is significantly greater than theinitial insertion force required to press a ball lead 16 into engagementwith the ball receiving contact 110. As a result, a ball grid arraysocket 10 employing the fourth embodiment of the ball receiving contact110 does not require a cover to ensure proper electrical engagementbetween the ball grid array package 12 and ball grid array socket 10.

Referring now to FIGS. 16A-16D, a method for mounting a plurality ofball leads 140 onto a ball grid array socket 142 is shown. Turning toFIG. 16A, a plurality of ball receiving contacts 144 are mounted withina plurality of corresponding apertures 146 which extend through thecarrier base 148. When properly mounted, the base 150 of each ballreceiving contact 144 is flush with the bottom surface 152 of thecarrier base 148. As a result, a contact grid 154 is created having thebase 150 of the ball receiving contacts 144 as contact areas and thenon-conductive bottom surface 152 of the carrier base 148 as non-contactareas.

Turning to FIG. 16B, the steps of inverting the carrier base 148 andscreening solder resist 156 onto the inverted carrier base 148 areshown. In particular, the carrier base 148 is inverted after the ballreceiving contacts 144 have been mounted within the apertures 146 of thecarrier base 148. Afterwards, a layer of solder resist 156 is screenedonto the inverted carrier base 148 through a stencil (not shown). Aplurality of apertures 158 remain after the solder resist screening stepand leave a portion of each base 150 of each ball receiving contact 144exposed.

Turning to FIG. 16C, the step of screening a sticky flux 160 into theapertures 158 is shown. In particular, a sticky flux 160 is screenedinto the apertures 158 and onto the bases 150 of the ball receivingcontacts 144 through a stencil (not shown).

Turning to FIG. 16D, the step of depositing the ball leads 140 onto thebase carrier 148 is shown. In particular, the ball leads 140 aredeposited onto the plurality of sticky flux regions 160 covering theformerly exposed portions of the bases 148 of the ball receivingcontacts 144. Afterwards, the inverted carrier 148 and eutectic solderball leads 140 combination is heated to seal the ball leads 140 to thecarrier base 148 through the solder resist 156 and electrically connectthe ball leads 140 to the bases 150 of the ball receiving contacts 144through the sticky flux 160.

Turning now to FIGS. 17A-17E, a second embodiment of the method formounting a plurality of ball leads 140 onto a ball grid array socket 142is shown. Turning to FIG. 17A, a plurality of ball receiving contacts144 are mounted within the corresponding plurality of carrier baseapertures 146 which extend through a carrier base 148. When properlymounted, each base 150 of each ball receiving contact 144 is flush withthe bottom surface 152 of the carrier base 148. As a result, a contactgrid 154 is created having the bases 150 of the plurality of ballreceiving contacts 144 as contact areas and a non-conductive bottomsurface 152 of the carrier base 148 as non-contact areas.

Turning to FIG. 17B, the steps of inverting the carrier base 148 anddepositing a dry resist 162 are shown. In particular, the carrier base148 is inverted after the ball receiving contacts 144 have been mountedwithin the apertures 146 of the carrier base 148. Afterwards, a layer ofdry resist 162 is deposited over the inverted carrier base 148 and thebases 150 of the mounted ball receiving contacts 144.

Turning to FIG. 17C, the step of etching the dry resist 162 isillustrated. In particular, apertures 158 are etched into the dry resist156 above a portion of each base 150 of each ball receiving contact 144.As a result, a portion of each contact base 150 is exposed.

Turning to FIG. 17D, the step of screening a sticky flux or solder paste160 into the apertures 158 is shown. In particular, a sticky flux 160 isscreened into the apertures 158 and onto the exposed portions of thebases 150 of the ball receiving contacts 144 through a stencil (notshown).

Turning to FIG. 17E, the step of depositing the ball leads 140 onto thecarrier base 148 is shown. In particular, eutectic solder ball leads 140are deposited onto the plurality of sticky flux or solder paste regions160 covering the formerly exposed portions of the bases 150 of the ballreceiving contacts 144. Afterwards, the eutectic solder ball leads 140and inverted carrier 148 combination are heated to seal the eutecticball leads 140 to the carrier base 148 through the dry resist 162 and toelectrically connect the ball leads 140 to the bases 150 of the ballreceiving contact 144 through the sticky flux 160.

Each of the above-described contacts can be formed from a planarsingle-thickness sheet of metal. The sheet is stamp formed as a blankwith necessary recesses being cut therein. Thereafter, the stamp formedblank is bent and shaped to produce the desired-shape contact.

As is readily apparent, the contacts disclosed herein can be readilymodified. For example, referring to FIG. 18, an alternative embodimentof the tulip-shaped ball receiving contact 46 is depicted and generallydesignated with the reference numeral 164. The construction of thecontact 164 is generally the same as the contact 46, except the downwardextending cantilevered blade 54 is modified. The length of materialwhich defines the cantilevered blade 54 with respect to the contact 46is shortened and bent to extend across the bottom opening of the splitcollar 48 to form the contact 164, and a solder ball 166 is mountedthereto. The solder ball 166 is for connection to a desired location.Also, other embodiments of the invention may be modified to be formedwith a solder ball in lieu of a ball lead.

Referring to FIGS. 19 and 20, transition pins are shown for use with anyof the above-described electrical contacts. A first embodiment of thetransition pin is shown in FIG. 19 and designated with the referencenumeral 168. The transition pin 168 is formed with a planar surface 170at one end for surface mounting onto the lead of an integrated circuit(IC). By example, the transition pin 168 is shown in FIG. 19 as beingmounted to a land L, but may be mounted to other types of leads known inthe art. The transition pin 168 is also formed with a body 172, having afrustoconical portion 173 and a cylindrical portion 175, from whichextends a truncated spade-shaped head 174. The transition pin 168 isgenerally cylindrical, defining circular cross-sections about the axis176. Preferably, the transition pin 168 is formed from a copper alloy,such as brass, to provide both strength and good conductive properties.Also, the head 174 of the transition pin 168 may be plated with goldover nickel to further enhance the conductive properties.

The truncated spade-shaped head 174 is formed with a planar free end 178which defines a diameter d₁. The largest diameter defined by thetruncated spade-shaped head 174 is designated by d₂ and is located adistance s₁ from the end 178. In the plane of intersection of the body172 and the head 174, the head 174 defines a diameter d₃ which is lessthan the overall dimensions of the cylindrical portion 175 of the body172. Preferably, the portion of the head 174 which lies between thediameter d₂ and the diameter d₃, shown in FIG. 19 as corresponding tothe length s₂ is spherically generated about the center of the diameterd₂ and with the same radius (one-half of d₂). The head 174 is taperedbetween the diameters d₁ and d₂. For ease of manufacturing, a portion ofthe head 174 below the diameter d₂ may also be spherically generated, inaccordance with the aforementioned characteristics, and caused to blendwith the tapering portion of the head 174. Preferably, the distance s₂is approximately three times as great as the distance s₁.

The diameter d₁ is dimensioned to be less than the openings defined bythe resilient arms of any of the aforementioned contacts. Thus, thetransition pin 168 may be initially inserted into one of theabove-described contacts without coming into contact therewith. Thediameter d₂ must be dimensioned large enough to be engaged or clasped byany of the above-described contacts. In reading the detaileddescriptions relating to any of the above-described contacts, thediameter d₂ of the transition pin 168 corresponds to the diameter of theball contact lead which is to be engaged by the respective contact.

With the relative dimensioning of the head 174 as described above, thetransition pin 168 provides for easy insertion. The taper of the head174 allows for gradual expansion of the engaged contact, eventuallyachieving full engagement. The elongated shape of the head 174, ascompared to the generally spherical shape of ball contact leads, doesnot interfere with engagement by a contact. When engaged by any of theelectrical contacts provided with a clasping mechanism, the claspingmechanism will engage the head 174 at points located between thediameters d₂ and d₃.

Referring to FIG. 20, the second embodiment of the transition pin isshown therein and generally designated with the reference numeral 180.The transition pin 180 is intended to convert a ball grid array package12 having relatively soft solder ball contact leads 16 from being anunsocketable package to a socketable package which can be received byany of the aforementioned sockets. The transition pin 180 is mountedinto and through an aperture 182 formed in a non-conductive adaptorboard 184. The transition pin 180 may be mounted into the adaptor board184 using any technique known by those skilled in the art, butpreferably press fitting. The number of transition pins 180 and,respectively, the number of apertures 182 formed in the adaptor board184 correspond to the number of ball contact leads 16 which are formedon the ball grid array package 12.

The transition pin 180 is formed with a truncated spade-shaped head 186,formed exactly as the truncated spade-shaped head 174 described abovewith regards to the transition pin 168. The transition pin 180 is alsoformed with a planar end 188, an elongated body 190, and an intermediateportion 192 which extends between the body 190 and the head 186. Theintermediate portion 192 includes a cylindrical section 194, having adiameter greater than the body 190, and a frustoconical section 196. Thecylindrical section 194 acts as a lock-in barb to prevent the transitionpin 180 from being loosened from the adaptor board 184. The cylindricalsection 194 presses tightly against or extends into the surface of theaperture 182. As with the transition pin 168, the transition pin 180 isgenerally cylindrically shaped and formed with circular cross-sectionsabout axis 198. Also, as with the transition pin 168, the transition pin180 is preferably formed from brass, and the head 186 may be plated withgold over nickel.

In use, the solder ball contact lead 16 is fused to the planar end 188of the transition pin 180. With the adaptor board 184 being secured tothe ball grid array package 12, the heads 186 of the transition pins 180may then be repeatedly urged into engagement with any of theabove-described contacts.

While the invention has been described with respect to severalembodiments, it is apparent that a variety of changes may be madewithout departing from the scope of the invention as defined by theappended claims.

For example, in lieu of the tapered clasping aperture 86 of the secondembodiment of the ball receiving contact 70 of the subject invention, anequivalent clasping mechanism such as a plurality of slits or a well maybe provided. Additionally, in lieu of the dry film 132 utilized in thefourth embodiment of the ball receiving contact 110 of the subjectinvention, a solder resist may be provided. Furthermore, in lieu of thesticky flux 160 and eutectic solder ball leads 140 of the first andsecond embodiments of the method of the subject invention, solder pasteand copper ball leads may be provided.

I claim:
 1. A conductive ball lead receiving contact comprising an upperball lead receiving portion formed for resiliently engaging a conductiveball lead, a lower contact portion, and a solder ball mounted to saidlower portion;wherein said contact is formed from a single sheet ofmetal with a tulip shape including: a split collar having an outersurface and an inner surface, said inner surface defining a channel,said split collar having a base portion extending across at least aportion of said channel, said base portion having a downwardly facingbottom surface; a plurality of resilient cantilevered leaves extendingupwardly from said split collar for receiving the conductive ball lead,said leaves spaced apart a distance less than the diameter of saidconductive ball; a plurality of cantilevered tangs extending downwardlyand radially from said split collar, each said cantilevered tang havinga free end spaced from said outer surface of said collar; and the solderball being mounted to said bottom surface of said base portion of saidsplit collar.
 2. The contact of claim 1, wherein said cantileveredleaves are generally V-shaped in configuration, each cantilevered leavehaving the apex of said V defining an intermediate projecting section.3. The contact of claim 1, wherein said tulip-shaped contact isheat-treated beryllium copper.
 4. A transition pin for surface mountingonto a lead of an integrated circuit, said transition pin for beingreleasably engaged by a resilient electrical contact, said transitionpin comprising:a planar first end for surface mounting onto the lead ofthe integrated circuit; a body extending from said first end; and atruncated spade-shaped head extending from said body, said head defininga plurality of varying diameter circular cross-sections along a centrallongitudinal axis, said axis being generally normal to said first end,said head having a planar free end spaced from said body along saidaxis, the largest diameter cross-section of said varying diametercross-sections being spaced along said axis from said free end a firstdistance and from said body a second distance, said first distance beingapproximately three times as great as said second distance, and saidhead having a frustoconical shaped portion extending from said free endand substantially coextensively with said first distance, wherein saidfirst end, said body and said head are unitarily formed from a singlematerial.
 5. A transition pin as in claim 4, wherein said singlematerial is a copper alloy.
 6. A transition pin as in claim 5, whereinsaid head is plated.
 7. An adaptor for mounting onto a ball grid arraypackage, said adaptor for repeated engagement and disengagement with asocket having resilient electrical contacts, said ball grid arraypackage having a plurality of conductive ball leads formed from a soldermaterial, said adaptor comprising:a non-conductive substrate having anupper surface, a lower surface and a plurality of apertures extendingtherebetween, the quantity of said apertures corresponding to thequantity of said conductive ball leads; and a plurality of transitionpins corresponding to the quantity of said apertures, each saidtransition pin being mounted in a single said aperture of saidnon-conductive substrate, each said transition pin having a planar firstend disposed coextensively with said upper surface of saidnon-conductive substrate, a body extending from said first end andthrough respective said aperture, and a truncated spade-shaped headextending from said body, said head defining a plurality of varyingdiameter circular cross-sections along a central longitudinal axis, saidaxis being generally normal to said first end, said head having a planarfree end spaced from said body along said axis, the largest diameter ofsaid varying diameter cross-sections being spaced along said axis fromsaid free end a first distance and from said body a second distance,said first distance being approximately three times as great as saidsecond distance, and said head having a frustoconical shaped portionextending from said free end and substantially coextensively with saidfirst distance, and wherein each said transition pin is unitarily formedfrom a single material.
 8. An adaptor as in claim 7, wherein saidtransition pins are formed from a copper alloy.
 9. An adaptor as inclaim 8, wherein said heads of said transition pins are plated.
 10. Anintegrated circuit assembly for repeated engagement and disengagementwith a socket having expandable, resilient electrical contacts, saidassembly comprising:a ball grid array package having a plurality ofconductive ball leads formed from a first material; a non-conductivesubstrate having an upper surface, a lower surface and a plurality ofapertures extending therebetween, the quantity of said aperturescorresponding to the quantity of said conductive ball leads; and aplurality of transition pins corresponding to the quantity of saidapertures, each said transition pin being mounted in a single saidaperture of said non-conductive substrate, each said transition pinhaving a planar first end disposed coextensively with said upper surfaceof said non-conductive substrate, a body extending from said first endand through respective said aperture, and a head extending from saidbody, each said transition pin being unitarily formed from a secondmaterial which is harder than said first material, wherein saidconductive ball leads are securely mounted to said first ends of saidtransition pins.
 11. An integrated circuit assembly as in claim 10,wherein said first material is solder, and said second material isbrass.
 12. An integrated circuit assembly as in claim 11, wherein saidheads of said transition pins are plated.
 13. An integrated circuitassembly as in claim 10, wherein said head of each said transition pinis formed with a truncated spade shape, each said head defining aplurality of varying diameter circular cross-sections along a centrallongitudinal axis, said axis being generally normal to said first end,said head having a planar free end spaced from said body along saidaxis, the largest diameter of said varying diameter cross-sections beingspaced along said axis from said free end a first distance and from saidbody a second distance, said first distance being approximately threetimes as greater as said second distance, and said head having afrustoconical shaped portion extending from said free end andsubstantially coextensively with said first distance.